In a study published in the journal Social Cognitive and Affective Neuroscience in 2011, researchers found that exposure to another person's stress sweat sharpened alertness.

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Meanwhile, a similar pilot study at the University of Missouri studied the use of Tai Chi as a method of cognitive rehabilitation for cancer survivors who had undergone chemotherapy.

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When all the students tackled the same problems a second time, those who had done a simple, boring task during a break had more creative ideas than those who were assigned a tough cognitive puzzle, those who rested, or those who didn't take a break, says the study, co-authored by Jonathan Schooler, a psychology professor at the University of California at Santa Barbara.

WSJ: Tactics to Spark Creativity

Dr. Rao is completing his own study comparing exercise and cognitive training in a different group of people.

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But another study on trust, by Judith Olson, a cognitive psychologist and professor of information and computer sciences at University of California, Irvine, showed that people who met virtually could predict behavior and establish trust if they had enough time.

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Previous studies have shown that quick, insightful solutions tend to be more correct than analytic solutions (at least, for the types of tasks in the study), and other studies have shown that a positive mood enhances overall cognitive performance.

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In the new government-funded study, volunteers ages 75 and older with either normal mental function or mild cognitive impairment took a twice-daily placebo or ginkgo biloba extract (for a total of 240 milligrams per day).

CNN: Study: Ginkgo doesn't cut dementia risk

Fish oil "seems to be healthy in general, and maybe for other things it's helpful, but it doesn't benefit cognitive function in a person with Alzheimer's, " says Ferris, who was not involved in the study.

CNN: Fish oil ingredient doesn't slow Alzheimer's